Air pollutants are any gas, liquid or solid substance that have been emitted into the atmosphere and are in high enough concentrations to be considered harmful to the environment, or human, animal and plant health.
Pollutants emitted directly into the air are called "primary pollutants." "Secondary" pollutants" are formed in the air, when they react with other pollutants . Ground-level ozone is an example of a secondary pollutant that forms when nitrogen oxides (NOx) and volatile organic compounds (VOCs) react in the presence of sunlight.
We come in contact with many kinds of air pollutants every day. Depending on the type and amount emitted, these pollutants may affect air quality at the local, regional, and/or global scale. For example, smoke from woodstoves or backyard burning, and motor vehicle exhaust are pollutant mixtures that affect air quality in our neighbourhoods and communities, and inside our homes. Â Smoke from forest fires or ground-level ozone can cover an entire region. Long-lasting pollutants can contribute to serious global problems, such as ozone depletion and climate change.
An air pollutant can become dangerous to our health when we are exposed to it for a long time, and also when we breathe in a large amount of it. Health effects can last for a short while (e.g., coughing) or become a long-term problem (e.g., lung and heart disease, cancer). Pollution can also cause death. The young, the elderly and those with pre-existing heart or lung disease are the most sensitive to the effects of air pollution.
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